Spacer is an important component for System-in-Package (SIP) application. Spacers may have various functions. For example, spacers may be inserted between stacked dies, so that the spacing between the stacked dies is increased for wire bonding request. The spacers may be plated with conductive layers, which may further be grounded. Accordingly, the spacers may be used for electrical shielding. When formed of or including thermal conductive materials, the spacers may also be used for dissipating the heat generated in the stacked dies. In addition, the spacers in the SIP packages may also be used for conducting electrical signals.